English: Early ship radio receiver designed by Alexander Stepanovich Popov, from around 1901. Popov in 1895 along with Guglielmo Marconi invented the first radio receivers. The receiver uses a coherer (center), a primitive radio wave detector consisting of a glass tube containing metal powder between two electrodes. When radio waves from the antenna are applied to the electrodes, the coherer becomes conductive. The coherer was also connected through a relay (lower left) to a battery and a paper tape recorder, and the current from the battery made a mark on the paper tape, or rang a bell. These signals were used to receive text messages in Morse code. The relay also activated an electromagnet (green objects, right) to move a metal arm to tap the coherer, disturbing the metal powder to restore it to a receptive state. The station is made of the exact calculations and drawings of Popov. By 1901 many ships of the Black Sea Fleet had been equipped with Popov's radio stations. Museum of Black Sea Fleet, Sevastopol, Ukraine